NAMING: elaborate why we don't use *_t and underscore prefixes

[cher-nov]

https://en.cppreference.com/w/c/language/identifier
https://www.gnu.org/software/libc/manual/html_node/Reserved-Names.html
https://stackoverflow.com/questions/224397/why-do-people-use-double-underscore-so-much-in-c
https://stackoverflow.com/questions/10687053/meaning-of-double-underscore-in-the-beginning

https://stackoverflow.com/questions/62734225/how-to-get-gcc-clang-to-error-on-reserved-identifiers